<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 100px;
            height: 100px;
            /* background: linear-gradient(135deg, rgba(245,245,4,1) 0%, rgba(196,30,92,1) 29%, rgba(249,55,109,1) 52%, rgba(227,49,158,1) 76%, rgba(255,0,7,1) 100%); */
            opacity: 1;
            background-color: blue;
            /* background-image: radial-gradient(circle, rgba(245,245,4,1) 0%, rgba(196,30,92,1) 29%, rgba(55,249,152,1) 52%, rgba(49,105,227,1) 76%, rgba(255,0,73,1) 100%); */
            /* border-radius: 50%; */
            animation: circle 3s linear 0s 1;
        }
        
        .box:hover{
        }

        /* 定义动画 */
        @keyframes circle {
            0%{
                opacity: 1;
                background-color: red;
                /* width: 100px; */
                /* transform: rotate(0deg); */
            }
            /* 50%{
                opacity: 0;
            } */
            100%{
                opacity: 1;
                background-color: blue;
                /* width: 500px; */
                /* transform: rotate(360deg); */
            }
        }
    </style>
</head>
<body>
    <div class="box"></div>
</body>
</html>